In the electrostatic spray coating of objects, powder is sprayed out of a spray opening of a spray device and given a positive or negative electrostatic charge, either immediately in front of this outlet opening or after this outlet opening. For this purpose, electrodes, referred to in the following as charging electrodes, are used, which are connected to an electrical high voltage in the range between 40 KV and 140 KV. The objects to be coated have a different electrical potential, preferably ground potential. The atomized powder particles move along electrical field lines which are generated by the high voltage between the charging electrode and the object to be coated. After a thin layer of powder has formed on the object to be coated, this layer repels subsequent powder particles because of its electrical charge that is, because both sets of powder particles are electrostatically charged in a like manner. As a result, only a limited layer thickness can be generated on the object to be coated. Furthermore, due to the reciprocal repulsion of the powder particles on the surface of the object to be coated, an unstable force ratio is created. This unstable force ratio has the result that the coated powder layer is not a smooth, flat coating surface that is formed, but rather a type of "hilly landscape," which forms a so-called "orange peel" when the layer is subsequently fired, and therefore should be prevented, if possible.
The electrostatic attraction characteristics of the object to be coated is different at the edges and corners as well as at openings of this object, as compared with large, flat large areas. Usually, corners and edges are coated less well or less thickly than adjacent larger surface areas. The powder particles fly around the edges of the outside circumference and around the edges of openings of the object to be coated, due to the effect of the electrostatic field, and are therefore drawn to the back of the object, because of its electrostatic attraction, so that the back of the object to be coated is also coated there. This can be called "electrical surrounding."
By using a counterelectrode which draws free ions out of the sprayed powder stream, the surface quality and the penetration capacity of the powder into depressions of the objects to be coated can be improved. Furthermore, a thicker powder layer can be applied to the objects to be coated, in a single spraying process, without an excessive amount of powder particles bouncing off the objects or being electrostatically repelled. In particular, an "orange peel"-like layer surface can be prevented.